High trans butadiene based elastomeric block copolymers and blends

ABSTRACT

Rubbery high trans-high vinyl diblock copolymers, blends of rubbery high trans copolymers and rubbery high vinyl polymers, and mixtures (alloys or blends) of said diblock copolymers, high trans copolymers and high vinyl polymers are useful in producing tire treads exhibiting good processibility, good rolling resistance, skid resistance and abrasion resistance. The high trans block or copolymer comprises a copolymer of butadiene-1,3 and styrene and/or isoprene and the high vinyl block or polymer comprises polybutadiene or copolymers of butadiene and styrene and/or isoprene. These di-block copolymers, copolymers and polymers are made by solution polymerization. The diblock copolymer may be made by copolymerizing butadiene and styrene and/or isoprene using a Ba, Ca or Sr alcoholate, R 2  Mg and R 3  Al to from about 60 to 95% conversion to a high trans block and then adding (optionally more Bd with or without Sty and/or isoprene) a strong Lewis base and a Na, K or Rb alkoxide and continuing the polymerization to completion to obtain the high vinyl block of the di-block copolymer.

This invention relates to high trans-1,4-butadiene based elastomeric orrubbery diblock copolymers and blends useful for making improved tiretreads.

It is an object of this invention to provide a high-trans-1,4-butadienebased diblock copolymer or blend useful in tire treads.

It is another object of this invention to provide a method for making ahigh trans 1,4-butadiene based diblock copolymer.

It is a further object of this invention to provide a tire with a treadof a high trans-1,4-butadiene based elastomer diblock copolymer andblends of the same.

These and other objects and advantages of the present invention willbecome more apparent to those skilled in the art from the followingdetailed description, examples and accompanying drawings in which

FIG. 1 compares the tread properties of HTSBR/HVSBR blends and otherHVSBR blends with respect to IPST (Instrumented British Portable SkidTester) wet skid coefficient versus Pico Index,

FIG. 2 compares the wet skid coefficients and Pico abrasion indices forblends of HTSBR/HVSBR and NR/MVSBRs (50/50),

FIG. 3 is a graph showing the temperature dependence of the loss tangentfor mechanical blends and

FIG. 4 is a vertical cross sectional view of a tire embodying thecompositions of the present invention.

HTSBR: High trans styrene-butadiene rubber

HVSBR: High vinyl styrene-butadiene rubber

Li-BR: Lithium polymerized butadiene

LVSBR: Low vinyl styrene-butadiene rubber

NR: Natural rubber

MVSBR: Medium vinyl styrene-butadiene rubber.

SUMMARY OF THE INVENTION

According to the present invention, novel styrene-butadiene diblockcopolymers are prepared having as one component low (not over about 8%)vinyl, high trans-1,4 polybutadiene placements (overall content of fromabout 75 to 85%) and as a second component high vinyl polybutadieneplacements (about 40 to 80%). Either this block copolymer alone, or ablend of the homopolymers comprising the block segments, leads toimproved tire tread compositions. Specifically, the compositions of thisinvention are of two general types: (1) block copolymers of the AB-type,[HTSBR (Tg, glass transition, less than about -70° C.) -b-HVSBR or HVBR(Tg greater than about -70° C. and not above about -35° C.) where brepresents block polymer], and (2) mechanical blends of HTSBR and HVSBRor HVBR (high vinyl butadiene rubber).

The all-synthetic tread compounds based on the materials of thisdisclosure have a unique combination of properties: good extrusionprocessibility, low rolling resistance, high traction and high abrasionresistance. The good traction properties are a result of the appropriatestructure of the high Tg segment (HVSBR), whereas the low Tg hightrans-1,4 segment of the HTSBR contributes abrasion resistance, strengthand reduced rolling resistance. The structural parameters that effectthese properties are the styrene content and polybutadienemicrostructure of the block or blend components, their molecular weightand the block or blend ratio. Polymers with different moleculararchitecture and molecular weight distribution (MWD) can readily beprepared using the polymerization processes described here.

The HTSBR is described in the prior art by having predominantly hightrans-1,4 structure together with extremely low vinyl contents (about 2to 4%). Accordingly, these polymers exhibit a low level of crystallinity(unstretched and uncompounded). They also show a substantial improvementin both cured and uncured properties of the rubbers obtained overrubbers prepared by other initiator (catalyst) systems such asorganolithiums.

The block copolymers and blends of this invention have a high trans SBR(high trans, low vinyl) component blended with, or molecularly bondedto, a high vinyl SBR or BR. The amount of HTSBR can vary from about 25to 80wt.% in the diblock copolymer, blend or mixture. The total overallbound styrene content in the block copolymer, blend or mixture variesfrom about 5 to 20 wt.% and the total overall vinyl content in the blockor blend ranges from about 30 to 60%. When used as the only rubbercomponent in a passenger tire tread compound, the elastomer compositionof this invention provides improved wear resistance and improvedtraction with nearly the same rolling efficiency (as measured bylaboratory instruments) as do blends of NR with solution SBR's (about50% vinyl).

The process for the preparation of HTSBR-b-HVSBR copolymers consists ofthe use of a barium salt of an alcohol, in combination with an organomagnesium compound and an organo aluminum compound or anorganomagnesium-organoaluminum complex, for co-polymerization ofbutadiene and styrene in cyclohexane to a conversion of from about 60 to95%, preferably about 85%, to form HTSBR (block A) followed by theaddition of more monomer(s) if desired, an alcoholate of sodium(preferred), potassium or rubidium or mixture thereof and a strong Lewisbase for the formation of HVSBR (block B). The resulting SBR has apredominantly random distribution of styrene units in each block. Thehigh content of trans-1,4 placements in block A gives rise to somecrystallinity as observed by DSC (Differential Scanning Calorimetry) andcrystalline melting temperatures that can be decreased to near or belowroom temperature (about 25° C.) by adjustments of the trans-1,4 contentand the level of styrene. The resulting polymers have reduced cold flowand excellent processibility.

There is evidence from molecular weight and MWD data of the diblockcopolymer that a high proportion of block polymer is formed with thiscatalyst system. Both the diblock copolymers as well as thecorresponding blends of HTSBR/HVSBR exhibit two transitions in the DSCcurves for both the uncured polymer and its black filled vulcanizate.The values of the glass transition temperatures correspond to therespective components (HTSBR and HVSBR) and indicate theirincompatibility.

For the HTSBR portion, described in this invention, part or all of thestyrene may be replaced with isoprene. For the HVSBR portion describedin this invention, the styrene monomer may be replaced withbutadiene-1,3; isoprene and styrene mixtures; or butadiene-1,3, isopreneand styrene mixtures. Under the polymerization conditions described forpreparing the HVSBR the isoprene develops high vinyl groups (1,2+3,4).

The HTSBR is made using a barium, magnesium and aluminum complex insolution in a hydrocarbon solvent.

For the blend, the HVSBR or HVBR is made using an anionic organolithiuminitiator and a strong Lewis base in solution in a hydrocarbon solvent.

Additionally, the HTSBR-b-HVSBR diblock copolymer may be used as analloying agent for the separately prepared HTSBR copolymer and the HVSBRcopolymer or HVBR.

In making the blends, the polymeric solutions can have antioxidantsadded, the polymerizations are terminated with an alcohol or water andthe solvent removed. The dried polymers are then mechanically (dry)blended or mixed (in a Banbury or on a rubber mill, etc.).Alternatively, the polymeric solutions can be terminated, and thepolymeric solutions can then be blended or mixed, antioxidants added,and solvent removed to obtain a dry rubber blend.

The HVSBR copolymer or HVBR polymer, when prepared with a mono-lithiumhydrocarbon initiator for use in the blends, can be chain extended toimprove processibility. The HTSBR used in the blends also has thecapability of being chain extended to increase molecular weight andbroaden molecular weight distribution.

Due to the nature of the initiators, promoters, cocatalysts,polymerization systems used, and possibly due to impurities, the blockcopolymers can contain some copolymers or homopolymers.

DISCUSSION OF DETAILS AND PREFERRED EMBODIMENTS

The barium (preferred), calcium or strontium alcoholate or alkoxide saltor mixture of such salts may be made by reacting an alcohol, optionallyadditionally including a small amount of water, with Ba, Ca and/or Srmetal. The reaction can be conducted in liquid NH₃ or amine solvent at atemperature of from about -100° C. up to the boiling point of thesolvent or above the boiling point under pressure. After the reaction,the NH₃ or amine can be removed from the salt by distillation, vacuumevaporation and solvent extraction. Methods of making the bariumalkoxide salts, such as barium t-alkoxide salts, which also will beapplicable to the corresponding Ca and Sr salts, are shown in U.S. Pat.Nos. 3,992,561; 4,260,519 and 4,260,712.

Examples of aliphatic alcohols to use to make the Ba, Ca and/or Sralkoxides or alcoholates are methanol, ethanol, propanol, isopropanol,n-butanol, cyclopentanol, cycloheptanol, cyclohexanol, s-butanol,t-butanol, allyl alcohol, pentanol, hexanol, octanol, and decanol and soforth and mixtures of the same. These alcohols can have from 1 to 10carbon atoms in each alkoxide moiety which may be the same or different.Examples of such alcoholates are calcium diethoxide,di(t-butoxy)strontium, di(t-butoxy) barium, di(isopropoxy)barium,di(cyclohexyloxy) barium and so forth. It is preferred to use a moreacidic alcohol like allyl alcohol in making the alkali metal salt suchas di(allyloxy)barium, barium diallyl oxide, since it is not necessaryto use ammonia or an amine to facilitate reaction between the metal andalcohol nor to conduct a separate step of removing the ammonia or amineto reduce the nitrogen content of the metal alcoholate before use as aco-initiator or co-catalyst.

The organoaluminum compounds used to the practice of the presentinvention are alkyl and cycloalkylaluminum compounds. These compoundscan be prepared by reacting aluminum metal with an olefin in thepresence of hydrogen. Another method, for example, comprises thereaction:

    2Al+3(CH.sub.3).sub.2 Hg→3Hg+2(CH.sub.3).sub.3 Al.

Other methods can be used. See "Aluminum Alkyls," Texas Alkyls,Copyright 1976 by Stauffer Chemical Company, Westport, Conn., 71 pagesincluding the bibliography shown therein and "Encyclopedia Of PolymerScience And Technology," Vol. 1, 1964, Interscience Publishers adivision of John Wiley & Sons, Inc., New York, Pages 807 to 822. Theseorganoaluminum compounds have the general formula R₃ Al where R is analkyl radical or cycloalkyl radical, which may be the same or different,of from 1 to 20, preferably of from 1 to 10, carbon atoms. Mixtures ofthese organoaluminum compounds can be used. Examples of such compoundsare trimethyl aluminum, triethyl aluminum (preferred), tri-n-propylaluminum, triisopropyl aluminum, pentyl diethyl aluminum,2-methylpentyl-diethyl aluminum, tri-n-butyl aluminum, triisobutylaluminum, dicyclohexylethyl aluminum, tri-n-pentyl aluminum, tri-n-hexylaluminum, tri-n-octyl aluminum, tri(2-ethylhexyl)aluminum,tricyclopentyl aluminum, tricyclohexyl aluminum,tri(2,2,4-trimethylpentyl)aluminum, tri-n-dodecyl aluminum andtri(2-methylpentyl)aluminum and the like.

The organomagnesium compounds used in the practice of the presentinvention are alkyl and cycloalkyl magnesium compounds. These compoundscan be prepared by the action of R₂ ^(I) Hg on magnesium, the reactionbeing facilitated by the presence of ether. They, also, may be preparedby allowing olefins to react under pressure at about 100° C. withmagnesium metal in the presence of hydrogen. Please see "OrganometallicCompounds," Coates et al, Vol. 1, 1967, 3rd Ed., Methuen & Co. Ltd.,London. These organomagnesium compounds have the general formula R₂ ^(I)Mg where R^(I) is an alkyl radical or cycloalkyl radical, which may bethe same or different, of from 1 to 20, preferably of from 1 to 10,carbon atoms. Mixtures of these organomagnesium compounds can be used.Examples of such compounds are dimethyl magnesium, diethyl magnesium,dipropyl magnesium, di-n-butyl magnesium, di-sec-butyl magnesium,di-n-amyl magnesium, methyl-ethyl magnesium, n-butyl ethyl magnesium,n-propylethyl magnesium, di-n-hexyl magnesium, dicyclohexyl magnesium,cyclohexylethyl magnesium, didecyl magnesium, di-ter-butyl magnesium anddidodecyl magnesium and the like. n-butyl ethyl magnesium andn-butyl-sec-butyl magnesium are preferred.

Organo Mg-Al complexes can be used instead of mixtures of Mg and Alcompounds. One method of preparation is to add the organoaluminumcompound to a reactor containing the reaction products of organichalides with magnesium in hydrocarbon solvent. After filtration of thereaction mixture, there is obtained a solution of the complex containinglittle soluble halides. Please see Malpass et al, "Journal ofOrganometallic Chemistry," 93 (1975), pages 1 to 8. These complexes willhave the general formula R_(m) Al_(n).R_(p) ^(I) Mg_(q) where the moleratio of Al to Mg is as set forth herein, where m, n, p and q arenumbers sufficient to satisfy the required valences of the radicals andatoms and where R and R^(I) are alkyl or cycloalkyl radicals, which maybe same or different, as described above.

In the catalyst composition the mole ratio computed as metal ofmagnesium to aluminum is from about 105:1 to 1.5:1, and the mole ratiocomputed as metal of barium, calcium and/or strontium to magnesium isfrom about 1:10 to 1:2.

Methods for making high trans butadiene-styrene rubbery copolymers usingthe alkali metal salts, organomagnesium compounds and organoaluminumcompounds are disclosed in U.S. Pat. Nos. 4,297,240; 4,302,568 and4,307,218. If it is desired to achieve quantitative polymerization inreasonable reaction times when making only HTSBR, then between about 80and 90% conversion of monomers to copolymer, a strong Lewis base,preferably N,N,N',N'-tetramethylethylene diamine (TMEDA), and analkoxide of Na, K, or Rb (preferably rubidium t-amylate to speed thereaction) are added to obtain 100% conversion in from about 5 to 6hours.

In making the high vinyl block attached to the high trans SBR blocksadditional butadiene-1,3 or butadiene-1,3 and styrene may be added tothe living high trans copolymerization media along with an alkali metalalcoholate or alkoxide and a strong Lewis base.

The alkali metal alcoholate or alkoxide used in making the high vinylportion of the block copolymer is a sodium (preferred), potassium, orrubidium alkoxide or mixture thereof where the organic moieties of thealkoxide group have from 3 to 6 carbon atoms. Examples of some alcoholsused to make these alkoxides are propyl alcohol, isopropyl alcohol,butyl alcohol, tert-butyl alcohol, tert-amyl alcohol, isoamyl alcohol,amyl alcohol, hexyl alcohol, cyclopentanol and cyclohexanol. Mixtures ofthese metal alkoxides can be used. Different alkoxides may require moreor less of the alkoxide to be used to obtain the desired results. Of thealkoxides it is preferred to use sodium t-amylate. It, also, ispreferred that the strong Lewis base be selected from the groupconsisting of tertiary aliphatic amines and aliphatic ethers andmixtures of the same. Examples of strong Lewis bases are triglyme(triethylene glycol dimethyl ether), tetraglyme, diglyme (diethyleneglycol dimethyl ether), TMEDA, dimethoxyethane and 1,2-dipiperidinoethane. Of these materials it is preferred to use TMEDA.

The alkali metal alcoholate and strong Lewis base are used in minoramounts by weight based on the weight of the monomers sufficient to getthe desired vinyl content of the HVSBR or HVBR block. Both are necessaryto get the desired high vinyl content when making a block copolymer inthe presence of (residual) initiator or catalyst compounds remainingfrom the high trans copolymerization. Without TMEDA, maximum vinylcontents of 40-45% are obtained when only Na t-amylate is used to modifythe Ba-Mg-Al catalyst or initiator system. With TMEDA and Na t-amylate,vinyl contents up to 80-85% are possible. The amount of vinyl structureis dependent primarily on Na/R₂ Mg mole ratio, and only shows a slightdependence of polymerization temperature (10°-50° C.) and/or TMEDA/R₂ Mgmole ratio (0.3 to 1.0).

The lithium anionic initiator used when a separately prepared HVSBR orHVBR is intended for blending or mixing should be a soluble mono- ordi-lithium hydrocarbon having from 2 to 40 carbon atoms. Examples ofsome lithium anionic initiators are isopropyllithium, n-butyllithium,sec-butyllithium, t-butyllithium, isobutyllithium, amyllithium,hexyllithium, ethylhexyllithium, tert-octyllithium, n-decyl-lithium,naphthyllithium, 4-butylphenyllithium, p-tolyllithium,4-phenylbutyllithium, cyclohexyllithium, 4-butyl-cyclohexyllithium,4-cyclohexyl-butyllithium, 1,10-dilithiodecane, 1,20-dilithioeicosane,1,4-dilithio-cyclohexane, 1,4-dilithio-2-butene, 1,8-dilithio-3-decane,1,2-dilithio-1,2-diphenyl-ethane, 1,2-dilithio-1,8-diphenyloctane,4,4'-dilithiobiphenyl, dilithiopolyisoprene (having from 2 to 8isoprenyl units) and dilithiopolybutadiene (having from 2 to 8butadienyl units) and the like and mixtures thereof. Preferably, theinitiator has the formula RLi where R is an alkyl group of from 2 to 10carbon atoms and mixtures thereof. It is even more preferred to usen-butyl lithium and/or sec-butyl lithium. The lithium compound is usedin a minor amount by weight, as compared to the weight of the monomers,sufficient to provide a high molecular weight rubbery polymer orcopolymer. In general there may be used from about 0.0003 to 0.001 moleof initiator computed as lithium per 100 grams of total butadiene-1,3and styrene and/or isoprene monomer(s). Dilithium or polyfunctionallyderived organolithium compounds such as are described in U.S. Pat. No.4,409,368 can also be used. In the separate organolithium initiatedpolymerization to make the HVSBR or HVBR by itself, the strong Lewisbase is used in an amount of from about 0.01 to 1% by weight based onthe weight of the monomers in the polymerization mixture.

Solvents for use during solution polymerizations are aliphatichydrocarbons like hexane, heptane, octane, nonane, decane, dodecane,cyclohexane, cycloheptane, cyclooctane and the like and mixturesthereof. Hexane and cyclohexane are preferred solvents to use. Insolvent polymerization it is preferred to operate on a basis of not overabout 15 to 20% polymer solids concentration in the solvent to enableready heat transfer, to facilitate stirring and to aid in processing.Temperatures used during polymerization are from about 25° to 80° C.Times will depend on the desired degree of conversion to copolymer butin general will be from about 4 to 6 hours.

Polymerizations of course, should be conducted in a closed reactor,fitted with a stirrer, heating and cooling means, with means to flushwith or pump in an inert gas such as nitrogen, neon, argon and so forthin order to polymerize under inert or non-reactive conditions, withmeans to charge monomers, solvent, initiators, cocatalysts andmodifiers, venting means and with means to recover the resultingcopolymer and so forth.

An active polymer chain extender or coupling agent for the lithiumpolymer of the blend, if used, can be SnX₄ where X is halogen, e.g., tinfluoride, chloride, bromide or iodide or mixture of the same. Stannicchloride or tin (IV) chloride is the preferred coupling agent. Othercoupling agents can be used such as SiX₄ and GeX₄. The coupling agent isused in an amount of not above about 50% of the stoichiometric amountrequired to react with all of the Li atoms in the lithium hydrocarboninitiated polymerizations. Divinyl benzene and diisopropenyl benzene ormixture thereof, also, can be used in small amounts for diblockcopolymers prepared with the Ba-Al-Mg initiators. Polymers prepared withlithium catalysts or initiators can be chain extended or branched alsowith divinyl benezene or diisopropenyl benzene. The coupling agent canserve partly to chain extend or branch the living copolymer or to formstar copolymers and is added after substantially complete conversion.These coupling agents are of help in preventing cold flow. However, inthe presence of acids used during rubber compounding the Sn-C bond, forexample, may be broken to some extent.

The polymerizations may be terminated by adding water, alcohol or otheragent to the polymeric solutions. Conversion of the metal ions tosulfates renders them passive. After the polymers have been recoveredand dried, a suitable antioxidant such as 2,6-di-tert-butyl-p-cresol orother antioxidant may be added to the same. However, the antioxidant maybe added to the polymeric solutions before they are stripped of solvent.

The di-block copolymers, blends and so forth produced by the methods ofthe present invention can be compounded and cured or vulcanized in thesame manner as other rubbery polymers. For example, they can be mixedwith sulfur or sulfur furnishing materials, peroxides, reinforcingcarbon blacks, SiO₂, TiO₂, Sb₂ O₃, stearic acid, ZnO, zinc stearate, rediron oxide, other rubber fillers and pigments, tetramethyl or ethylthiuram disulfide, benzothiazyl disulfide and rubber extending orprocessing mineral or petroleum oils and the like. Stabilizers,antioxidants, UV light absorbers and other antidegradants can be addedto these polymers. They, also, can be blended with other elastomeric orrubbery polymers like natural rubber, cis-polyisoprene, butyl rubber,cis-polybutadiene, butadiene-acrylonitrile copolymer,butadiene-styrene-acrylonitrile terpolymers, polychloroprene, solutionor emulsion SBR, polyurethane elastomers and so forth. The addition tothe polymers of this invention of small amounts, e.g., about 10 phr ofchloro- or bromo-butyl rubber may improve further the wet frictioncoefficient of a tire tread embodying these polymers.

While the rubbery di-block copolymers and blends of the presentinvention are particularly useful in making a carbon black reinforcedcompounded tire tread for a pneumatic tire such as a bias, belted biasor radial passenger car tire, they can be used in other applications.For example, the di-block copolymers and blends produced by the methodsof the present invention, also, can be used in making truck tires,off-the-road tires, protective coatings for fabrics, athletic (tennis)balls, bushings (silentblocs), weather strips, windshield wiper blades,body and engine mounts for automobiles, gaskets, belts, hose, shoe solesand electric wire and cable insulation, and as plasticizers andpolymeric fillers for other plastics and rubbers. With large amounts ofsulfur, hard rubber products can be made.

In making tires, they are built in the customary fashion in which a tiretread of a vulcanizable rubbery polymeric composition of this inventionis applied to a green tire carcass and cured or vulcanized in a mold.The vulcanizable polymeric tread composition can be extruded orotherwise formed and vulcanized (pre-cured). The pre-cured tread stockcan then be applied to a cured, cleaned and adhesive coated cured tirecarcass and cured to the same (as in re-treading). The rubbercomposition, also, can be prepared as a master batch.

The following examples will serve to illustrate the present inventionwith more particularly to those skilled in the art.

The polymerizations used to make the polymers of the Examples werecarried out in argon atmospheres in capped glass bottles fitted withrubber gasket inner liners. Solvents were purified by passing theliquids through columns of 5 Å molecular sieves (Linde). Butadiene-1,3(99 mol %) was purchased from Phillips Petroleum Company. Purificationwas accomplished by passing the material through columns of 3 Åmolecular sieves. Styrene was purchased from Gulf Oil Chemical and ElPaso Products, Tex., and purged with a stream of nitrogen.

In charging styrene and butadiene-1,3 polymerizations with Ba-Mg-Al, theorder of addition of materials was solvent first, then monomer(s), nextthe Mg-Al alkyls, (triethyl aluminum and butyl ethyl magnesium) and thenthe barium salt, barium di(allyloxide) (Step 1). In preparing diblockpolymers, butadiene-1,3 immediately followed by Na t-amylate and TMEDA(Step 2) were added to the solution of polymeric carbanions formed inStep 1 above.

The copolymer composition and percent polybutadiene microstructure weredetermined by IR (Infrared analysis) and from ¹³ C NMR (Nuclear MagneticResonance) for certain polymers. The microstructure values determinedfrom IR and ¹³ C NMR were essentially identical. The vinyl content wasdetermined using the 905 cm⁻¹ IR absorption band. High performance gelpermeation chromatography (HPGPC) was carried out on the polymers usinga Waters Gel Permeation Chromatograph. Solutions at 1 wt.% were injectedonto columns at a flow rate of 1 ml/minute. The instrument oven and thedifferential refractometer were at 50° C. The column set configurationused, as designated by Waters Associates, was

    1×10.sup.6 Å+1×10.sup.5 Å+1×10.sup.4 Å+1×10.sup.3 Å.

All thermal transitions were obtained by DSC using a heating rate of 20°C./minute. Glass transition temperatures were determined from themidpoint of the inflection in the plot of differential heat flow withtemperature in the heating curve at a heating rate of 20° C./minute,obtained after first cooling the sample from 125° C. to -150° C.

TREAD COMPOUND FORMULATION

Tread rubber compositions were prepared according to the formulationshown in Table I, below. Oil content was varied from 5 to 15 phr (partsper hundred parts of rubber) to provide Shore A hardness values of 62±2.The rubber compounds were mixed on a two-roll, 12-inch mill and thencured with N-tert-butyl-2-benzothiazole sulfenamide (TBBS)/sulfur,whereas HTSBR blends and block copolymers were cross-linked with aN-cyclohexyl-2-benzothiazole sulfenamide (CBS)/sulfur system.

                  TABLE I                                                         ______________________________________                                        TREAD Vulcanizate                                                             Compound Formulation                                                                                   phr                                                  ______________________________________                                        Polymers                   100                                                N-339 Black (High Abrasion Furnace Carbon Black)                                                         45                                                 Circosol 4240/45XH Oil (naphthenic oil)(Sun Oil)                                                         10 ± 5                                          Zinc Oxide                  3                                                 Stearic Acid               2.5                                                Antioxidant a,p-phenylene diamine                                                                        1.2                                                N--tert-butyl-2-benzothiazole sulfenamide (TBBS) or                                                      Variable                                           N--cyclohexyl-2-benzothiazole sulfenamide (CBS) and                                                      (about 3.                                          Sulfur                     to 7.)                                             ______________________________________                                    

HTSBR/HVSBR blends in tread compounds (Table I) exhibit outstandingprocessing properties. This refers to mill blending, ingredientdispersion and extrusion. At nearly the same compound Mooney viscosity(60) and shear rate (100 sec.⁻¹), a tread compound containing a blend ofHTSBR/HVSBR (30/70), see Run No. 16 of this application, showedviscosity and relaxed die swell, as measured by a MonsantoProcessability Tester at 100° C., 0.059 inch capillary L/D=5, that wereboth 16% lower than a corresponding tread compound containing emulsionSBR 1500.

The extrusion characteristics, as measured by Garvey Die Extruder (ASTMD2230-83), of the above blend are compared to SBR 1500 in Table IA. Itcan be seen from the values of the Garvey Die Extrusion indices that theblend gave a smoother surface appearance. The weight/length ratio of theGarvey Die for zero tension extrusion was higher for SBR 1500 which isconsistent with its observed higher die swell.

                                      TABLE IA                                    __________________________________________________________________________    Garvey Die Extrusion Data                                                              Rating (1)        Output (1 min)                                     Elastomer                                                                              Swelling                                                                           Edge                                                                             Surface                                                                            Corners                                                                            Wt.                                                                              Length                                                                            Wt/Length                                   __________________________________________________________________________    HTSBR/HVSBR                                                                            4    4  4    4    22 33  0.67                                        (Run No. 16)                                                                  SBR 1500 2    3  3    3    39 35  1.11                                        __________________________________________________________________________     (1)-On a scale of 1-4; higher values represent a better rating           

TREAD VULCANIZATE PROPERTIES

These were determined as follows:

Loss Tangent Delta (Tan δ)

Tan δ was measured by means of an Instrumented Yerzley Oscillograph(IYO) at room temperature (ca.25° C.) and 5 Hertz. The YerzleyOscillograph is a good predictor of twin-roll rolling resistance of tiretread material formulations. The lower the tan δ value, the lower therolling resistance.

Wet Skid Coefficient of Friction

An instrumented British Portable Skid Tester (IPST) was used to measurethe wet coefficient of friction (μ-wet) on a smooth concrete surface.All wet-skid coefficient values are relative to a normalized standardμ-wet value of 0.600 for a 65/35 E-SBR/cis-BR carbon black filled treadvulcanizate formulation. The test shows good correlation of μ-wet withwet tire traction data (peak wet traction at 96.6 km/hour). The higherthe μ-wet, the better the traction performance on a wet concrete road.E-SBR: Emulsion styrene butadiene copolymer rubber, ca. 23.5% styrene.cis-BR: ca. 93% cis-polybutadiene.

Pico Abrasion Index

This test was run as described in ASTM D2228.

Dynamic Mechanical Tester

Loss tangent was measured on double-lap shear samples with a MaterialTesting System (MTS) at 40 Hz and 5% strain.

Blends

In the blends in the examples the polymer and copolymers weremechanically (dry) blended.

EXAMPLE 1

A HTSBR-b-HVSBR diblock copolymer (Table II, Run 1) was prepared asfollows: A Ba-Mg-Al initiator (described in U.S. Pat. No. 4,297,240) wasused to copolymerize butadiene and styrene in cyclohexane at 60° C. to aconversion of 72% in 5 hours (see Table II). The resulting solutioncontained a mixture of unreacted monomers and polymer carbanions ofHTSBR (6 wt. % styrene). To form the HTSBR-b-HVSBR diblock copolymer, anadditional quantity of butadiene and solutions of Na t-amylate and TMEDAin cyclohexane were charged to the reactor containing the abovenon-terminated solution of HTSBR. The carbanions of HTSBR were used toinitiate the copolymerization of butadiene with styrene to 94%conversion. HPGPC chromatograms of the diblock copolymer and thecorresponding HTSBR precursor were used to establish the formation ofthe diblock copolymer. A certain fraction of HTSBR and/or HVSBR ispresent along with block copolymer. About 75% by weight of blockcopolymer was formed based on number-average molecular weights of HTSBRand block copolymer.

                                      TABLE II                                    __________________________________________________________________________    Preparations.sup.a of a HTSBR-b-HVSBR Diblock                                 Copolymer with Ba-Mg-Al                                                          Diblock                                                                              Pzn. Modifier.sup.c      mM/100 g %                                 Run                                                                              Copolymer                                                                            Temp.,                                                                             Na        Monomers.sup.d                                                                          Monomers Conv.                                                                              Wt. % Styrene                                                                           %                  No.                                                                              Composition.sup.b                                                                    °C.                                                                         t-amylate                                                                          TMEDA                                                                              (grams)   Ba Mg Al (hrs.)                                                                             Charged                                                                            Found                                                                              Vinyl              __________________________________________________________________________    -- HTSBR  60   --   --   Bd (38.1) 0.18                                                                             0.57                                                                             0.04                                                                             72   14.2 6     3                                          Styrene (6.3)      (5)                               1  HVSBR  50   0.44 0.35 Unreacted -- -- -- 94   --   7    56                                          Monomers (from     (1)                                                        Step 1):                                                                      Sty (4.4)                                                                     Bd (8.0)                                                                      Additional                                                                    Bd (55.0)                                                                     Total                                                                         Bd (63.0)                                            __________________________________________________________________________     .sup. a polymerized in cyclohexane (338 g)                                    .sup.b ratio (HTSBR/HVSBR) = 45/55 (charged), 34/66 (found)                   .sup.c mM per 100 g monomers, mole ratios of 0.77(Na/Mg) and 0.61             (TMEDA/Mg)                                                                    .sup.d total Bd = 93.1 grams and styrene = 6.3 grams                          Bd = butadiene1,3                                                        

EXAMPLE 2

HTSBR and HVSBR rubbers for making blends were prepared as follows:HVSBR (10% styrene, 60% vinyl) was prepared in hexane at 30° C. withn-BuLi complexed with TMEDA. The resulting copolymer was chain-extendedwith SnCl₄. HTSBRs were prepared in hexane with a barium alcoholate incombination with an organomagnesium and organoaluminum complex (seeExample 1, above and Runs 4, 5 and 6). In this preparation, the finalconversion of a monomer mixture of butadiene/styrene (90/10) to polymerwas 89% in 6 hours (70° C./4 hrs, then 82° C./2 hrs). The mole ratios ofbarium salt to dialkylmagnesium and dialkylmagnesium to triethylaluminumwere 0.33 and 3.9, respectively.

In another preparation a mixture in cyclohexane of Rb t-amylate andTMEDA was added to a solution of carbanions of HTSBR obtained at 85%conversion after 4.5 hrs polymerization time at 65° C. Polymerization ofthe unreacted butadiene and styrene continued to 100% conversion in onlyone additional hour. The resulting polymer (see Run 6-1 in Table IV,Example 3) contained both HTSBR and medium vinyl SBR (15 wt.%), mainlyas a diblock polymer. The mole ratios of Rb salt to R₂ Mg and TMEDA toR₂ Mg were 2.8 and 1.3, respectively.

EXAMPLE 3

Characterization data of three AB-type diblock styrene-butadienecopolymers (Runs 1, 2 and 3), prepared according to Example 1, are givenin Table III, below. Variations in diblock copolymer structure wereobtained by varying the amount of Na t-amylate relative to fixed levelsof TMEDA and dialkylmagnesium. Vinyl content in HVSBR (column 7, TableIII) increased from 56 to 72% as the mole ratio of Na/R₂ Mg increasedfrom 0.8 to 1.3 at fixed levels of TMEDA and R₂ Mg (TMEDA/R₂ Mg=0.6).Without TMEDA, vinyl content is only 20% for a mole ratio of Na/R₂ Mgequal to 1.0. Table IV, below, provides corresponding characterizationdata of three mechanical blends (Runs 4, 5, 6 and 6-1) of HTSBR andHVSBR, prepared according to Example 2. Additional structural data ofvarious solution SBR's (Runs 7-15) which may be used in blends with NRor with each other are given in Table V, below. HTSBR (Run 7) isincluded for comparative purposes.

In the block copolymers as well as the mechanical blends of thisinvention, two distinct individual glass transitions are observed in theDSC thermograms, corresponding to the respective block or blendcomponents. Black filled vulcanizates containing these rubbers showsimilar transitions.

                                      TABLE III                                   __________________________________________________________________________    Characterization Data of Uncompounded and Uncured                             HTSBR-b-HVSBR Polymers                                                        Polymer Composition                     Tg, °C.                        HTSBR           HVSBR             Crystalline                                                                         By DSC                                Run                                                                              %    %   %   %    %   %   Wt. %                                                                              Melting                                                                             (midpoint)                                                                              --Mw/--Mn                   No.                                                                              Styrene                                                                            Trans                                                                             Vinyl                                                                             Styrene                                                                            Trans                                                                             Vinyl                                                                             HTSBR.sup.a                                                                        Temp., °C.                                                                   HTSBR                                                                              HVSBR                                                                              (by HPGPC)                  __________________________________________________________________________    1  6    82  3   7    23  56  34   21    -78  -46  2.47                        2  5    82  3   7    15  72  39   21    -80  -31  2.23                        3  7    77  4   5    23  57  45    8    --        2.46                        __________________________________________________________________________     .sup.a total wt. % HTSBR (as block copolymer and homopolymer)                 Mw/Mn = H.I. or heterogeneity index                                      

                                      TABLE IV                                    __________________________________________________________________________    Characterization Data of Uncompounded and Uncured Comparative                 Blends of HTSBR and HVSBR                                                     Blend Composition                   HTSBR                                     HTSBR           HVSBR         Tg, °C.                                                                      --Mw/--Mn    HVSBR                        Run                                                                              %    %   %   %    %   Wt. %                                                                              By DSC                                                                              (By   --Mn   --Mw/--Mn                                                                            --Mn                  No.                                                                              Styrene                                                                            Trans                                                                             Vinyl                                                                             Styrene                                                                            Vinyl                                                                             HTSBR                                                                              (midpoint)                                                                          HPGPC)                                                                              (Osmometry)                                                                          (By HPGPC)                                                                           (Osmomotry)           __________________________________________________________________________    4  5    82  3   13   52  34   -80, -43                                                                            1.87  101,000                                                                              1.86   --                    5  5    82  3   10   60  40   -80, -40                                                                            1.87  101,000                                                                              1.67   167,000               6  6    80  3   11   60  45   -81, --                                                                             2.07   98,000                                                                              1.69   197,000               6-1                                                                              11   75  8   10   60   35# -77, -40                                                                            3.58  --     2.29   199,000               __________________________________________________________________________     #This product consists of 85 wt. % HTSBR (5% sty, 81% trans, 3% vinyl) an     15 wt. % MVSBR (44% sty, 41% trans, 34% vinyl) because conversion was         carried to 100%. MSVBR from HTSBR portion totals 5.25 phr in blend of         HTSBR/HVSBR A(35/65).                                                    

                  TABLE V                                                         ______________________________________                                        Characterization Data of Uncompounded and Uncured                             Solution SBR's Which May Be Used In Blends                                    With NR Or With Each Other                                                    ______________________________________                                        Run    SBR                                                                    No.    % Styrene      % Trans  % Vinyl                                        ______________________________________                                         7      5             82        3                                              8      8             51       10                                              9      7             42       20                                             10     19             51        9                                             11      9             36       40                                             12     24             42       31                                             13     15             34       44                                             14     13             30       52                                             15     11             26       60                                             ______________________________________                                             Tg, °C.                                                           Run  By DSC    --Mn         --Mw/--Mn                                                                              ML 1 + 4                                 No.  (midpoint)                                                                              (Osmometry).sup.d                                                                          (By HPGPC)                                                                             (100° C.).sup.e                   ______________________________________                                         7.sup.a                                                                           -79       101,000      1.87     52                                       8    -83       125,000      1.91     58                                        9.sup.b                                                                           -78        125,000.sup.c                                                                             1.62     --                                       10.sup.                                                                            -72       163,000      2.69     65                                       11.sup.                                                                            -61        150,000.sup.c                                                                             1.46     --                                       12.sup.b                                                                           -52       174,000      1.87     55                                       13.sup.b                                                                           -47       169,000      1.60     55                                       14.sup.b                                                                           -40       --           1.86     55                                       15.sup.b                                                                           -37       197,000      1.69     61                                       ______________________________________                                         .sup.a crystalline melting temperature was 26° C.                      .sup.b coupled with tetravalent Sn                                            .sup.c expected molecular weight based on grams polymer/moles initiator       .sup.d Number average molecular weight by vapor phase osometry                .sup.e Mooney viscosity, large rotor                                     

EXAMPLE 4

The data in Table VI, below, compare cured tread properties of blends ofHVSBR and HTSBR with comparative blends containing LVSBR of low styrenecontents or BR, Run 18, prepared with an organolithium initiator system.In Run 16, HTSBR obtained at 89% conversion (see Example 2, Run 4) wasblended with HVSBR. In Run 16a, HTSBR-b-MVSBR obtained at 100%conversion (see Example 2, Run 6a) was blended with HVSBR. It should benoted that HVSBR blends containing HTSBR as well as HTSBR-b-MVSBR havelower than δ values with combinations of wet friction coefficient andPico abrasion index, adjustable by HTSBR content as shown in FIG. 1,that are improved relative to the blends containing low vinyl SBR or BR.These results indicate that the HVSBR blends with HTSBRs, HVSBR blendswith HTSBR-b-HVSBR diblock copolymers and mixtures thereof, of thisinvention have lower rolling resistance with a superior combination ofabrasion resistance and wet traction.

                                      TABLE VI                                    __________________________________________________________________________    Comparison of Tread Vulcanizate Properties                                    of HVSBR Blends Containing HTSBR and                                          Other Solution Rubbers                                                        Blend Composition                                                             LV Solution Rubbers                                                                          HVSBR          Tensile                                         Run                                                                              %    %   %   %    %   Wt. %                                                                              Strength                                                                           Tan δ                                                                       μ- Wet                                                                         Pico                               No.                                                                              Styrene                                                                            Trans                                                                             Vinyl                                                                             Styrene                                                                            Vinyl                                                                             HVSBR                                                                              (MPa)c                                                                             IYO IPST                                                                              Index                              __________________________________________________________________________    16.sup.                                                                          6    80  3   11   60  70   16.2 .173                                                                              .635                                                                              111                                16.sup.a                                                                         11   75  8   10   60  65   15.8 .186                                                                              .612                                                                               95                                17.sup.                                                                          8    51  10  10   61  70   15.0 .193                                                                              .581                                                                              101                                18.sup.b                                                                         0    54  9   11   60  70   13.9 .197                                                                              .564                                                                              109                                19.sup.                                                                          5    82  3   10   60  60   17.7 .202                                                                              .590                                                                              126                                20.sup.a                                                                         7    42  20   6   62  60   17.7 .206                                                                              .601                                                                               99                                __________________________________________________________________________     .sup.a Compounded with 50 phr N351 carbon black (high structure, high         modulus) instead of 45 phr N339 carbon black                                  .sup.b Polybutadiene                                                          .sup.c Megapascal                                                        

EXAMPLE 5

A medium vinyl SBR (Run 11) was prepared according to Example 2 withnearly the same total bound styrene and vinyl contents as a 30/70HTSBR/HVSBR blend. The tread vulcanizate properties in Table VII, below,show that the blend of this invention has substantially higher wet skidresistance at nearly the same combination of tan δ and Pico index(compare Runs 16 and 11).

The data in this table show a higher tensile strength for theHTSBR/HVSBR blend than the diblock of LVSBR-b-HVSBR (Run 22, preparedwith BuLi and Na t-amylate in the first step followed in the second stepby a charge of TMEDA and more butadiene-1,3 and styrene). Again, theblend has higher wet skid resistance with nearly the same loss tangentand Pico index.

                                      TABLE VII                                   __________________________________________________________________________    Comparison of Tread Vulcanizate Properties                                    for a HTSBR/HVSBR Blend; a                                                    Medium Vinyl SBR; and a LVSBR-b-HVSBR                                                         Average    Tensile                                            Run             Composition                                                                              Strength                                                                           Tan δ                                                                       μ- Wet                                                                         Pico                                  No.                                                                              Structure    % Styrene                                                                           % Vinyl                                                                            (MPa)                                                                              IYO IPST                                                                              Index                                 __________________________________________________________________________    16 HTSBR/HVSBR Blend.sup.a                                                                    9     43   16.2 .173                                                                              .635                                                                              111                                   11 MVSBR        9     40   14.1 .170                                                                              .547                                                                              108                                   22 (8 Sty/15 V/45 trans)-b-(8                                                                 8     42   12.7 .162                                                                              .616                                                                              110                                      Sty/60 V/25 trans).sup.b                                                   __________________________________________________________________________     .sup.a blend of (6 styrene/3 vinyl)/(11 styrene/60 vinyl), 30/70              .sup.b wt. % LVSBR (8 styrene/15 vinyl/45 trans) = 40%                   

EXAMPLE 6

When compared to blends of NR with high vinyl SBR's (see Runs 24, 27 and30, Table VIII, below), all-synthetic elastomeric blend compositionscontaining HTSBR/HVSBR have improved wear resistance (high Pico index)at three blend ratios (30/70, Run 16; 40/60, Run 25 and 45/55, Run 28)evaluated while maintaining an acceptable combination of tan δ and wettraction. The data in Table VIII also compare tread vulcanizateproperties for similar polymers of HTSBR-b-HVSBR (Runs 23, 26 and 29).They also have higher Pico index values, but have slightly higher valuesof loss tangent than NR blends containing HVSBR.

Run 31 in Table VIII shows the utility of using a HTSBR-b-HVSBR (62/38)block copolymer, as a polymeric alloying agent, in a blend with amixture or blend of HTSBR and HVSBR. Again, the data indicate that animproved set of tread properties was obtained.

                  TABLE VIII                                                      ______________________________________                                        Comparison of Tread Vulcanizate Properties of                                 HTSBR/HVSBR Blends and HTSBR-b-HVSBR Block Copolymers                         with Mechanical Blends of NR/HVSBR                                            Tread Rubber Composition                                                      ______________________________________                                                                              Wt. %                                   Run  Low Tg Polymer        High Tg Polymer                                                                          Low Tg                                  No.  (Sty/Trans/Vinyl)     (Sty/Vinyl)                                                                              Polymer                                 ______________________________________                                        16.sup.a                                                                           (6/80/3)      +       (11/60)    30                                      23.sup.b                                                                           (6/82/3)      - b -    (7/56)    34                                      24.sup.                                                                            NR            +       (13/52)    34                                      25.sup.a                                                                           (6/80/3)      +       (11/60)    40                                      26.sup.b                                                                           (5/85/3)      - b -    (7/72)    39                                      27.sup.                                                                            NR            +       (10/60)    40                                      28.sup.a                                                                           (6/80/3)      +       (11/60)    45                                      29.sup.b                                                                           (7/77/4)      - b -    ( 5/57)   45                                      30.sup.                                                                            NR            +       (10/60)    45                                      31.sup.c                                                                           (6/80/3) + [(2/80/3) - b - (13/65)]+ (11/60)                                                             40                                            ______________________________________                                                Tensile                                                               Run     Strength Tan δ μ-Wet                                                                            Pico                                       No.     (MPa)    IYO         IPST  Index                                      ______________________________________                                        16      16.2     .173        .635  111                                        23      15.3     .205        .562  114                                        24      16.6     .183        .613   98                                        25      14.8     .184        .614  120                                        26      13.6     .214        .613  106                                        27      16.0     .180        .637   93                                        28      18.3     .210        .573  126                                        29      19.2     .230        .545  127                                        30      16.5     .176        .636   93                                        31      16.8     .173        .622  113                                        ______________________________________                                         .sup.a mechanical blend of HTSBR and HVSBR                                    .sup.b HTSBRb-HVSBR diblock copolymer                                         .sup.c HTSBR/HTSBRb-HVSBR/HVSBR (25/25/50)                               

EXAMPLE 7

Vinyl containing SBR copolymers and styrene-butadiene block copolymers,prepared using an organolithium initiator system and limited to vinylcontents greater than about 8-10%, when blended 50/50 with NR, are saidto be superior to the use of solution SBRs alone and to emulsion SBR/NRblends in tire treads. The properties of various solution SBRs, havingvinyl contents ranging from 9 to 60%, have been compared in blends withNR versus the HTSBR/HVSBR blends of this invention. The results shown inTable IX, below, demonstrate that the blend (Run 16) has nearlyequivalent tan δ to the blends of NR (Runs 32-35) with the benefit of animproved combination of wet friction coefficient and abrasion resistanceas shown in FIG. 2.

The combined properties of low rolling resistance and high wet fractionare also demonstrated by the dynamic mechanical behavior of these treadvulcanizates. The temperature dependence of the loss tangent of treadvulcanizates of a HTSBR/HVSBR blend (Run 16) is compared in FIG. 3 witha NR/MVSBR blend (Run 33) tread compound. At 60° C. both vulcanizatesshow nearly the same tan δ, indicating comparable rolling resistance. Ata low temperature, (0° C.) and below, the HTSBR/HVSBR blend shows highertan δ, indicating higher wet traction than NR/MVSBR.

                                      TABLE IX                                    __________________________________________________________________________    Comparison of Tread Vulcanizate Properties                                    of Blends of HTSBR/HVSBR with                                                 Various Solution SBR's Blended with NR                                                              Tensile                                                 Run               Blend                                                                             Strength                                                                           Tan δ                                                                       μ- Wet                                                                         Pico                                       No.                                                                              Tread Rubber Composition                                                                     Ratio                                                                             (MPa)                                                                              IYO IPST                                                                              Index                                      __________________________________________________________________________    16 HTSBR.sup.a + (11 Sty/60 Vinyl)                                                              30/70                                                                             16.2 .173                                                                              .635                                                                              111                                        32 NR + (10 Sty/60 Vinyl)                                                                       30/70                                                                             12.6 .211                                                                              .627                                                                               95                                        33 NR + (15 Sty/44 Vinyl)                                                                       50/50                                                                             17.3 .173                                                                              .618                                                                              107                                        34 NR + (24 Sty/31 Vinyl)                                                                       50/50                                                                             19.8 .194                                                                              .610                                                                              109                                        35 NR + (19 Sty/9 Vinyl)                                                                        50/50                                                                             17.4 .172                                                                              .539                                                                              114                                        __________________________________________________________________________     .sup.a HTSBR (6% styrene/80% trans/3% vinyl)                             

As shown in FIG. 4 of the drawings which is illustrative of a pneumatictire, especially a radial passenger tire, the tire comprises a carbonblack reinforced sulfur vulcanized tread portion 1 in which all of therubber of the tread can comprise the diblock SBR copolymer or polymerblends or mixtures of the same of the present invention. The tire alsocontains sidewalls 2, white sidewalls 3, beads 4 and belts 5.

We claim:
 1. A composition of matter comprising a rubbery solutionpolymer selected from the group consisting ofI. a high transcopolymer-high vinyl polymer diblock copolymer, II. a blend of a hightrans copolymer and a high vinyl polymer and III. a blend or mixture ofa high trans copolymer-high vinyl polymer diblock copolymer, a hightrans copolymer and a high vinyl polymer a. where said high transcopolymer is a copolymer of butadiene-1,3 and at least onecopolymerizable monomer selected from the group consisting of styreneand isoprene, has a Tg of less than about -70° C., has an overallcontent of about 75 to 85% trans units and not over about 8% vinyl unitsin the butadiene segments and comprises about 25 to 80% by weight of thecomposition, b. where said high vinyl polymer is at least one polymerselected from the group consisting of homo polybutadiene and copolymersof butadiene-1,3 and at least one monomer selected from the groupconsisting of styrene and isoprene, has a Tg of greater than about -70°C. and not above about -35° C. and has about 40 to 80% vinyl units inthe butadiene segments and c. where in said composition the totaloverall amount of styrene and/or isoprene is from about 5 to 20% byweight and the total overall amount of vinyl groups is from about 30 to60%.
 2. A composition according to claim 1 comprising a high transstyrene-butadiene copolymer rubber-high vinyl styrene-butadienecopolymer rubber diblock copolymer.
 3. A composition according to claim1 comprising a blend of a high trans styrene-butadiene copolymer rubberand a high vinyl styrene-butadiene copolymer rubber.
 4. A compositionaccording to claim 1 comprising a blend or mixture of a high transstyrene-butadiene copolymer rubber-high vinyl styrene-butadienecopolymer rubber diblock copolymer, a high trans styrene-butadienecopolymer rubber and a high vinyl styrene-butadiene copolymer rubber. 5.The method which comprises, (I) polymerizing under inert conditions in ahydrocarbon solvent at a temperature of from about 25° to 80° C.butadiene-1,3 and at least one monomer selected from the groupconsisting of styrene and isoprene with a catalyst in a minor effectiveamount sufficient to polymerize said monomers to obtain a polymer, saidcatalyst comprising (1) an alcoholate selected from the group consistingof barium alcoholate, calcium alcoholate and strontium alcoholate andmixtures thereof, (2) an organolaluminum compound selected from thegroup consisting of alkyl and cycloalkyl aluminum compounds and mixturesof the same in which the organic moieties have from 1 to 20, preferablyfrom 1 to 10, carbon atoms and (3) an organomagnesium compound selectedfrom the group consisting of alkyl and cycloalkyl magnesium compoundsand mixtures of the same in which the organic moieties have from 1 to20, preferably from 1 to 10, carbon atoms, and complexes of (2) and (3)where the mole ratio computed as metal of barium, calcium and/orstrontium to magnesium is from about 1:10 to 1:2 and where the moleratio computed as metal of magnesium to aluminum is from about 105:1 to1.5:1 to obtain a high trans copolymer block and to a conversion of fromabout 60 to 95%, preferably about 85%, and (II) then adding to theresulting living high trans copolymer or carbanions additional monomerselected from the group consisting of butadiene-1,3 and a mixture ofbutadiene-1,3 and at least one monomer selected from the groupconsisting of styrene and isoprene, and minor amounts by weight, basedon the weight of the monomers, sufficient to obtain a high vinyl contentpolymer block, of at least one strong Lewis base and at least onealkoxide selected from the group consisting of sodium, potassium andrubidium alkoxides having from 3 to 6 carbon atoms in the organicmoieties of the alkoxide group and continuing the polymerization toobtain a high trans copolymer-high vinyl polymer diblock copolymera.where said high trans copolymer block has a Tg of less than about -70°C., has an overall content of from about 75 to 85% trans units and notover about 8% vinyl units in the butadiene segments and comprises about25 to 80% by weight of the diblock copolymer, b. where said high vinylpolymer block has a Tg of greater than about -70° C. and not above about-35° C. and has about 40 to 80% vinyl units in the butadiene segments ofthe high vinyl block, and c. where in said diblock copolymer the totaloverall amount of styrene and/or isoprene is from about 5 to 20% byweight and the total overall amount of vinyl groups is from about 30 to60%.
 6. The method according to claim 5 where in (I) the monomers arebutadiene-1,3 and styrene and where in (II) the monomers arebutadiene-1,3 and styrene.
 7. The method according to claim 6 where in(I), (1) is barium di(allyloxide), (2) is triethyl aluminum and (3) isbutyl ethyl magnesium and where in (II) said strong Lewis base istetramethylethylenediamine and said alkoxide is sodium t-amylate.
 8. Themethod which comprises, polymerizing under inert conditions in ahydrocarbon solvent at a temperature of from about 25° to 80° C.butadiene-1,3 and at least one monomer selected from the groupconsisting of styrene and isoprene with a catalyst in a minor effectiveamount sufficient to polymerize said monomers to obtain a polymer, saidcatalyst comprising (1) an alcoholate selected from the group consistingof barium alcoholate, calcium alcoholate and strontium alcoholate andmixtures thereof, (2) an organolaluminum compound selected from thegroup consisting of alkyl and cycloalkyl aluminum compounds and mixturesof the same in which the organic moieties have from 1 to 20, preferablyfrom 1 to 10, carbon atoms and (3) an organomagnesium compound selectedfrom the group consisting of alkyl and cycloalkyl magnesium compoundsand mixtures of the same in which the organic moieties have from 1 to20, preferably from 1 to 10, carbon atoms, and complexes of (2) and (3)where the mole ratio computed as metal of barium, calcium and/orstrontium to magnesium is from about 1:10 to 1:2 and where the moleratio computed as metal of magnesium to aluminum is from about 105:1 to1.5:1 to obtain a high trans copolymer block and to a conversion of fromabout 60 to 95%, preferably about 85%, and then adding to the resultingliving high trans copolymer or carbanions minor amounts by weight, basedon the weight of the monomers, of at least one strong Lewis base and atleast one alkoxide selected from the group consisting of sodium,potassium and rubidium alkoxides having from 3 to 6 carbon atoms in theorganic moieties of the alkoxide group and continuing thecopolymerization to completion.
 9. The method according to claim 8 wherethe monomers are butadiene-1,3 and styrene.
 10. The method according toclaim 9 where (1) is barium di(allyloxide), (2) is triethyl aluminum and(3) is butyl ethyl magnesium, where said strong Lewis base istetramethylethylenediamine, where said alkoxide is rubidium t-amylateand where the conversion is 100% in from about 5 to 6 hours.